In the plastics industry it has been recognized that blending of different polymers can result in a composition that has properties that are superior to those of each individual component. However, one of the limitations of blending polymeric materials is that most polymer structures are immiscible (e.g., incompatible) with other (structurally different) polymers and when combined, the individual materials form phases that result in a product that does not have superior properties relative to the individual components.
Specifically, immiscible polymer blends are not thermodynamically stable. In addition, the post-mixing processing such as molding or annealing, can affect the blend morphology and reduce or eliminate any benefits of blending. In order to overcome this, an additive is often combined with the polymeric blended materials.
In other instances, when two structures are joined together in block or graft copolymer structures, the polymers oftentimes separate into phases at a microscopic scale. When the constituents of the separate phases are covalently linked to the polymer backbone, gross separation is eliminated and it is easier to produce compatible polymers, particularly block and graft copolymers. In block polymers, this micro-phase separation can result in improved material properties.
The sulfonated polymers described herein may be sulfonated by any variety of methods, including but not limited to, the specific exemplary sulfonation methods described herein. Sulfonation generally refers to an organic chemical reaction that leads to the formation of a carbon-sulfur bond. When the reacting compound contains an aromatic ring, sulfonation at the aromatic ring by the reactive (sulfonating) compound usually occurs by replacing a hydrogen atom on the aromatic ring by a sulfonic acid residue functional group by means of an electrophilic aromatic substitution reaction. However, with particular compounds, such as phenylalkanoic acids, sulfonation may occur on the carbon adjacent to the carboxyl group, rather than on the aromatic ring. In contrast to aromatic nitration or other electrophilic aromatic substitutions, aromatic sulfonation is reversible.
Sulfonation of aromatic compounds utilizing sulfur trioxide, sulfuric acid, chlorosulfonic acid, or acetyl sulfate as the sulfonating agent have been accomplished in the past with varying degrees of success. (Gilbert, Chem. Rev. 62: 549-589 (1962); German Patent No. DE 580,366). The processes can be expensive, difficult, and oftentimes results in incomplete sulfonation of the compound, especially for large molecular weight oligomers or polymers. (Gilbert, supra).
Moreover, the technique of using sulfur trioxide as the sulfonating agent results in the generation of considerable amounts of undesired side-products during the course of the sulfonation reaction and subsequent work-up due to the high reactivity of the sulfur trioxide. The sulfonation side-products are frequently difficult to remove and may contaminate the final sulfonated polymer product. (Gilbert, supra).
Thus, existing methods that describe using sulfur trioxide as a sulfonating reagent to sulfonate compounds have resulted in non-uniform, incomplete sulfonation, and a high rate of formation of undesirable side-products. Further, sulfonation reactions utilizing sulfur trioxide and other reagents have, in some cases, resulted in limited ability to create sulfonated products, particularly with respect to sulfonating large molecular polymers. Moreover, excess sulfuric acid and acetic acid that result from the use of acetyl sulfate can only be removed by way of an elaborate, and expensive, absorption or extraction cleaning processes or other means. Furthermore, the use of sulfuric acid introduces water into the reaction, which can alter the ability of the reaction components to effectively solvate the polymer target. The introduction of water into the reaction through the use of sulfuric acid also prohibits sulfonating polymers with labile, or hydrolytically unstable, functional groups or moieties.
Sulfonated block copolymers have been produced by traditional sulfonation. See, for example, U.S. Pat. No. 3,577,357. The resulting copolymer was characterized as having the general configuration A-B-(B-A) 1-5, wherein each A is a non-elastomeric sulfonated monovinyl arene polymer block and each B is a substantially saturated elastomeric alpha-olefin polymer block, said block copolymer being sulfonated to an extent sufficient to provide at least 1% by weight of sulfur in the total polymer and up to one sulfonated constituent for each monovinyl arene unit. The sulfonated polymers could be used in their produced form, or in their acid, alkali metal salt, or ammonium salt (including complex amine) forms.
The sulfonation of unsaturated styrene-diene block copolymers has also been attempted. See, for example, U.S. Pat. No. 3,642,953. In this particular example, polystyrene-polyisoprene-polystyrene was sulfonated using chlorosulfonic acid in diethyl ether. However, the sulfonic acid functionality incorporated into the polymer promotes oxidation, and the residual alkene (C═C) sites left in the polymer backbone are prone to rapid oxidation, restricting the utility of these polymers. Thus, the membranes produced with these polymers were found to be weak and could not be stabilized to make them practical for shaping or forming.
Similarly, in other examples, sulfonation of a t-butylstyrene/isoprene random copolymer and styrene/butadiene copolymer has been performed, but the products are prone to oxidative degradation, and lack flexibility to be formed or shaped. See, for example, U.S. Pat. Nos. 3,870,841 and 6,110,616. Finally, a blend of an aliphatic hydrocarbon oil and a functionalized, selectively hydrogenated block copolymer to which has been grafted sulfonic functional groups has been prepared. See U.S. Pat. No. 5,516,831.
There is, therefore, a need in the art for novel and effective methods for the improvement of processing, mechanical properties, and dimensional stability of sulfonated polymers, and blended materials comprising sulfonated polymers (to include, macromolecules, copolymers)